Resistive Second-Harmonic Impedance Continuous Class-F Power Amplifier With Over One Octave Bandwidth for Cognitive Radios

A novel methodology for designing highly-efficient broadband harmonic-tuned power amplifiers (PAs) with more than one octave bandwidth is presented in this paper. Continuous class-F power amplifiers with resistive second-harmonic impedance is for the first time analyzed and employed in a multi-sub-band mode to enhance the bandwidth of a conventional continuous class-F PA. The load-pull method is employed at both fundamental and harmonic frequencies, and the simplified real frequency technique algorithm is used to design and synthesize the PA matching networks. Experimental results show that the fabricated PA operates from 525 to 1325 MHz, with drain efficiency over 70% and output higher than 39 dBm. Digital predistortion is applied to the PA and the adjacent channel power ratio is improved to more than -40 dBc.